1.Field of the Invention
The present invention relates to a prosthetic bone filler and a process for the production of the same.
2. Description of the Related Art
Recently, when a lacking site was produced in a bone due to bone diseases, injury and other causes, an artificial prosthetic material or prosthetic filler is embedded in the lacking site of the bone. The lacking sites of the bone to which the prosthetic filler is applied include a wide variety of bone sites such as cranium, vertebra and articulate. Furthermore, the materials used as a prosthetic filler include ceramic materials such as alumina or hydroxyapatite, metallic materials such as Ti or Co--Cr alloy, and resinous materials such as polymethyl methacrylate or high density polyethylene. Among these prosthetic fillers, the fillers made of alumina, hydroxyapatite and other ceramic materials have less flexibility than the bone itself, because they are solely made from the ceramic material. Due to less flexibility when only a small amount of bone surrounds the site in which the ceramic filler is embedded, the bone surrounding the filler can be sometimes destroyed when an external mechanical force or load is applied to the body having the embedded filler. To solve this problem, use of the prosthetic filler produced by mixing a ceramic material with a resinous material has been proposed. For example, Japanese Unexamined Patent Publication (Kokai) No. 5-237180 discloses a bone bonding device including a core material, produced upon extrusion molding of a mixture of hydroxyapatite, a biologically degradable polymer, and a melt-molded coating of polylactic acid. However, due to lack of porosity, the bone bonding device does not exhibit ventilation properties, and hence, lacks bio-compatibility. Further, Japanese Unexamined Patent Publication No. 7-8547 discloses a prosthetic filler including a porous block of sintered calcium phosphate compound having impregnated in an inner and surface portion thereof a biologically absorbing polymeric substance. However, the prosthetic filler also does not exhibit bio-compatibility; and the mechanical characteristics substantially depend upon the ceramic material used, i.e., a calcium phosphate compound instead of a polymeric substance.